The present invention relates to installing fuel rods in a nuclear fuel assembly skeleton, and it is particularly applicable to fuel assemblies in which the skeleton includes guide tubes interconnecting removable end fittings and carrying grids that delimit cells distributed at the nodes of a regular array and designed to receive the rods.
Such assemblies are used in nuclear reactors that are cooled and moderated by water, in particular by pressurized water.
An apparatus is already known for installing fuel rods in such a skeleton, of the type which comprises receiving means for receiving a skeleton without end nozzles, interposed between a magazine for storing fuel rods in alignment with locations in the skeleton for receiving the rods, and a displacement mechanism for displacing pull bars longitudinally towards the magazine and away from the magazine, the pull rods being terminated by clamps for grasping the rods to be inserted in the skeleton.
This applies in particular when the cells in the grids are distributed in a square array, with the displacement mechanism often being provided with the same number of pull bars as there are cells in a layer and enabling an entire layer of rods to be installed simultaneously in the skeleton. After the rods in one layer have been inserted, the mechanism is displaced transversely relative to the layer through a distance equal to the pitch between layers and is used to load a new layer of rods.
The shape of the clamps on the pull bars is such that, while they are being displaced towards the magazine through the grids, they run the risk of damaging the springs and/or the projections provided on the plates that constitute the grids for the purpose of holding the rods in place.
To avoid this risk, it is common practice to place caps having an externally tapered shape on the clamps before inserting the pull bars into the skeleton. The caps are removed when the clamps are in an intermediate position between the outlets from the skeleton and the magazine.
At present, these operations are performed manually. They are lengthy, particularly the operation of installing the caps. They require an operator to remain in the vicinity of the fuel rods. Unfortunately, greater and greater use is being made of rods that contain reprocessed fuel and/or plutonium, thereby running the risk of irradiating the operators.